www.pudn.com > h263_.rar > Getbits.cpp

// Getbits.cpp: implementation of the CGetbits class. 
// 
////////////////////////////////////////////////////////////////////// 
 
#include "stdafx.h" 
#include "视频编解码器.h" 
#include "Getbits.h" 
 
#ifdef _DEBUG 
#undef THIS_FILE 
static char THIS_FILE[]=__FILE__; 
#define new DEBUG_NEW 
#endif 
 
 
extern CFile h263file; 
extern ldecode *ld; 
CGetbits::CGetbits() 
{ 
 
} 
 
CGetbits::~CGetbits() 
{ 
 
} 
 
static unsigned int msk[33] = 
{ 
  0x00000000,0x00000001,0x00000003,0x00000007, 
  0x0000000f,0x0000001f,0x0000003f,0x0000007f, 
  0x000000ff,0x000001ff,0x000003ff,0x000007ff, 
  0x00000fff,0x00001fff,0x00003fff,0x00007fff, 
  0x0000ffff,0x0001ffff,0x0003ffff,0x0007ffff, 
  0x000fffff,0x001fffff,0x003fffff,0x007fffff, 
  0x00ffffff,0x01ffffff,0x03ffffff,0x07ffffff, 
  0x0fffffff,0x1fffffff,0x3fffffff,0x7fffffff, 
  0xffffffff 
};  //最多可以取出32位比特数 
 
void CGetbits::initbits() 
{ 
  ld->incnt = 0;  //比特数为零 
  ld->rdptr = ld->rdbfr + 2048;//把缓冲区的头地址赋给指针 
  ld->bitcnt = 0; 
 
} 
 
void CGetbits::fillbfr() 
{ 
 int l; 
 
  ld->inbfr[0] = ld->inbfr[8]; 
  ld->inbfr[1] = ld->inbfr[9]; 
  ld->inbfr[2] = ld->inbfr[10]; 
  ld->inbfr[3] = ld->inbfr[11]; 
 
  if (ld->rdptr>=ld->rdbfr+2048) 
  { 
    l = h263file.Read(ld->rdbfr,2048);//装入字节 
    ld->rdptr = ld->rdbfr; 
    if (l<2048) 
    { 
      if (l<0) 
        l = 0; 
      while (l<2048)   /* Add recognizable sequence end code */ 
      { 
        ld->rdbfr[l++] = 0; 
        ld->rdbfr[l++] = 0; 
        ld->rdbfr[l++] = (1<<7) | (SEC<<2); 
      } 
    } 
  } 
 
  for (l=0; l<8; l++) 
    ld->inbfr[l+4] = ld->rdptr[l]; 
 
  ld->rdptr+= 8; 
  ld->incnt+= 64; 
 
} 
 
unsigned int CGetbits::showbits(int n) 
{ 
  unsigned char *v; 
  unsigned int b; 
  int c; 
 
  if (ld->incntinbfr + ((96 - ld->incnt)>>3); 
  b = (v[0]<<24) | (v[1]<<16) | (v[2]<<8) | v[3];//取4个字节 
  c = ((ld->incnt-1) & 7) + 25; 
  return (b>>(c-n)) & msk[n]; 
 
} 
 
unsigned int CGetbits::getbits(int n) 
{ 
  unsigned int l; 
  l = showbits(n); 
  flushbits(n); 
  return l; 
} 
 
unsigned int CGetbits::getbits1() 
{ 
  return getbits(1); 
} 
 
void CGetbits::flushbits(int n) 
{ 
  ld->bitcnt+= n; 
  ld->incnt-= n; 
  if (ld->incnt < 0) 
    fillbfr(); 
}